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United States Patent |
6,090,341
|
Vodrahalli
|
July 18, 2000
|
Method and system for extracting and refining gold from ores
Abstract
A process and system and for extracting and refining gold from ores using
relatively benign and inexpensive chemicals, fewer process steps, and
permitting the recycling and re-use of process chemicals. The invention is
preferably implemented as a two part process. In a first part process,
gold is extracted from the ore and dissolved in a chemical solution to
form a gold complex. The chemical solution preferably includes a KI and
I.sub.2. Optionally, Isopropyl alcohol is mixed with the KI and I.sub.2 to
serve as an accelerant. In a second part process, the complex is reduced
to gold from the solution, preferably by one of two methods. The first
method precipitates the gold complex by washing and decomposing of the
gold complex to form pure gold. The second method electrolytically plates
the gold from the gold complex solution onto a cathode to obtain pure
gold.
Inventors:
|
Vodrahalli; Nagesh K. (Cupertino, CA)
|
Assignee:
|
Hickman; Paul L. (Los Altos Hills, CA)
|
Appl. No.:
|
879851 |
Filed:
|
June 20, 1997 |
Current U.S. Class: |
266/101; 266/170 |
Intern'l Class: |
C22B 003/02 |
Field of Search: |
266/101,170
75/741
|
References Cited
U.S. Patent Documents
4859293 | Aug., 1989 | Hirano et al. | 75/741.
|
5026420 | Jun., 1991 | Kubo | 75/712.
|
5051128 | Sep., 1991 | Kubo | 75/712.
|
5542957 | Aug., 1996 | Han et al. | 75/744.
|
5948140 | Sep., 1999 | Vodrahalli | 75/741.
|
Primary Examiner: Wyszomierski; George
Attorney, Agent or Firm: Hickman Stephens Coleman & Hughes, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of co-pending U.S. Provisional Patent
Application No. 60/020,539, filed Jun. 25, 1996, the disclosure of which
is incorporated herein by reference.
Claims
What is claimed is:
1. An apparatus for extracting gold from ore comprising:
a source of ground ore having interstitial gold;
a source of an aqueous chemical solution including at least two species of
chemicals, where a first species is an alkali/alkaline halide, and where a
second species is the corresponding halogen;
an insulated reaction chamber operating at a reaction chamber temperature
and adapted to receive said ground ore and said chemical solution, thereby
causing at least some of said interstitial gold to form a gold complex of
the halogen in said aqueous solution;
a heater for heating said reaction chamber to said reaction chamber
temperature;
a holding tank coupled to said reaction chamber to receive said aqueous
solution;
a cooling system coupled to said holding tank to lower the temperature of
said aqueous solution to less than said reaction chamber temperature to
form a precipitate including gold;
a filtration chamber coupled to said holding tank to receive said aqueous
solution and said precipitate;
a source of water coupled to at least one of said holding tank and said
filtration chamber to convert said gold complex in said precipitate into
gold iodide; and
a decomposer for decomposing said gold iodide into gold.
2. An apparatus for extracting gold from ore as recited in claim 1 wherein
said first species is selected from the group consisting of potassium,
sodium, barium, and calcium, and wherein said halide is selected from the
group consisting of iodide, bromide, and chloride.
3. An apparatus for extracting gold from ore as recited in claim 1 wherein
said second species is selected from the group consisting of iodine,
bromine, and chlorine.
4. An apparatus for extracting gold from ore as recited in claim 1 further
comprising a mixer disposed within said reaction chamber.
5. An apparatus for extracting gold from ore as recited in claim 1 wherein
said reaction chamber temperature is controllably maintained between about
25.degree. C. and about 100.degree. C.
6. An apparatus for extracting gold from ore as recited in claim 1 wherein
said reaction chamber temperature is controllably maintained between about
50.degree. C. and about 60.degree. C.
7. An apparatus for extracting gold from ore as recited in claim 1 wherein
said heater is selected from the group consisting of immersion heaters and
electro-resistive heating elements.
8. An apparatus for extracting gold from ore comprising:
a source of ground ore having interstitial gold;
a source of an aqueous chemical solution including at least two species of
chemicals, where a first species is an alkali/alkaline halide, and where a
second species is the corresponding halogen;
an insulated reaction chamber operating at a reaction chamber temperature
and adapted to receive said ground ore and said chemical solution, thereby
causing at least some of said interstitial gold to form a gold complex of
the halogen in said aqueous solution;
a pre-heater coupled to said reaction chamber for heating said chemical
solution to said reaction chamber temperature;
a holding tank coupled to said reaction chamber to receive said aqueous
solution;
a cooling system coupled to said holding tank to lower the temperature of
said aqueous solution to less than said reaction chamber temperature to
form a precipitate including gold;
a filtration chamber coupled to said holding tank to receive said aqueous
solution and said precipitate;
a source of water coupled to at least one of said holding tank and said
filtration chamber to convert said gold complex in said precipitate into
gold iodide; and
a decomposer for decomposing said gold iodide into gold.
9. An apparatus for extracting gold from ore as recited in claim 8 further
comprising a sprayer for spraying said chemical solution onto said ground
ore.
10. An apparatus for extracting gold from ore as recited in claim 8 further
including a containment vessel disposed around said reaction chamber, said
containment vessel being capable of providing a shaking motion to said
reaction chamber and further capable of containing any said chemical
solution that may escape from said reaction chamber.
11. An apparatus for extracting gold from ore as recited in claim 8 wherein
said chemical solution further includes isopropyl alcohol.
Description
TECHNICAL FIELD
This invention relates to gold ore extraction and refining processes, and
systems implementing such processes.
BACKGROUND ART
In far ancient times, the only source of gold was relatively pure elemental
gold that was found in the form of nuggets and powder. Some thousands of
years ago, however, it was discovered that gold could be extracted from
ore by a process known as mercury amalgamation. This process was based
upon the fact that gold particles wetted by mercury adhere to each other
and to mercury coated copper plates. For many centuries, this process was
the only method used for extracting from ores. While the percentage of
gold recovered by a mercury amalgamation process varies with the type of
ore, it is a relatively inefficient process leading to a considerable loss
of gold.
The amalgamation process remained dominant until the 1890's, when cyanide
processes gained favor due to the dangers of mercury amalgamation (i.e.
slow death by mercury poisoning), the relative inefficiency of the
amalgamation process, and the scarcity and high cost of the required
mercury. The cyanide processes was first used in South Africa--the largest
producer of gold in the world --and is still the main gold extraction
process used to this day.
The cyanide process was a vast improvement over the amalgamation process in
terms of safety, cost, and efficiency. In this process, the gold in finely
ground ore is dissolved by treating it with a very dilute solution of
sodium cyanide or the less expensive calcium cyanide plus lime and oxygen
from air. The mixture is held for some hours in large tanks equipped with
agitators. The chemical reaction yields a water solution of gold cyanide
and sodium cyanoaurite. This solution of gold is treated to remove oxygen,
and is then clarified and mixed with zinc dust to precipitate the gold and
the other metals, such as silver and copper, that were dissolved by the
cyanide. The precipitate is then treated with dilute sulfuric acid to
dissolve residual zinc plus most of the copper. The residue is washed,
dried, and melted with fluxes (materials used to promote fusion of the
gold and silver and to dissolve the remaining copper). The operation may
be repeated to flux off more base metal. The remaining gold and silver
alloy, called dore, is then cast into molds for assay.
In FIG. 1, a prior art cyanide process 10 for extracting gold from ore
begins with a step 12 of mining the ore. Next, in a step 14, the ore is
ground to a sand-like consistency. In a step 16, a dilute mixture of NaCN,
lime, and oxygen is added to the finally ground ore and is agitated in a
large tank. This produces a water solution of gold cyanide and sodium
cyanoaorite. The solution may also include silver and gold cyanides. Next,
in a step 18, the oxygen is removed and a zinc dust is added to cause a
precipitation of the gold from the solution. Along with the gold, silver
and copper are also precipitated. In a step 20, H.sub.2 SO.sub.4 is added
to dissolve the zinc and copper. This produces an alloy known as dore,
which is essentially an alloy of gold and silver. Dore can be up to about
96% pure gold, with the majority of the remainder being silver. Next, a
purification process such as a Wohlwill process 22 or a Miller process 24
is used to create essentially pure gold. Both of these processes are well
known to those skilled in the art. The Wohlwill process can create 99.95%
pure gold, while the Miller process can create 99.5% gold purity. The
Wohlwill process is an electrolytic process wherein essentially pure gold
coats a cathode, and wherein impurities such as silver form chlorides and
remain near the anode. Typically, Pt and Pd also dissolve in the
electrolyte. In the Miller process, silver and other metals are converted
to chlorides by passing chlorine though molten dore, and then are poured
off or volatized. The Miller process creates a purity of only about 99.5%,
since it is stopped before the gold converts into a chloride.
Cyanide processes have been well developed over the past century. However,
these processes have a number of recognized deficiencies. For one, the use
of cyanide is extremely hazardous and the resulting effluents are damaging
to the environment. Further, it will be noted that the cyanide processes
involve a large number of process steps, including a series of
separations, alloying steps and final purification steps. These processes
also involve the use of a number of chemicals, some of which are quite
expensive, and a considerable expenditure of energy in the large number of
process steps. The cyanides processes are therefore considered too
expensive for use with low grade ores, and limit potential production due
to the slowness and cost of the total process.
The standard gold extraction processes principally use dangerous and
expensive chemicals like the cyanides, and have many steps resulting in a
complex process. They also require extensive purification processes after
extraction. It is therefore desirable to create a process that uses more
benign chemicals and uses simpler processes, thus having the potential to
reduce the overall cost of extracting and refining of gold.
In U.S. Pat. No. 5,221,421 of Leibovitz et al., a controlled etching
process for performing fine-geometry conductive gold circuit lines on a
substrate is disclosed for use in the electronics industry. Briefly, the
disclosed invention is concerned with the production of fine geometry
electronic circuitry by controlling the gold content in the etchants. This
requires reducing the dissolved gold content in the etchants when the gold
content begins to rise. Failure to reduce the gold content in the etchants
will affect process control. The reduction in gold content in the etchants
is achieved by recovering a dissolved gold complex compound (AuI.KI.sub.3)
from the etchant, thereby restoring the etchant for continuous etching of
the fine geometry gold circuit lines. The recovered complex is further
converted to AuI and subsequently to Au. Leibovitz et al. also propose to
reduce the gold content in the etchants by removing gold electrolytically.
Therefore, the Leibovitz et al. process teaches the removal of gold from a
etchant solution to permit the etchant solution to be reused. However,
this process as disclosed for providing fine electronic circuitry is not
be suitable for the mass production of gold from gold ores in that it is a
slow, controlled process used to maintain etchant purity and not a fast,
bulk process for economically producing large quantities of gold.
Therefore, this slow controlled process used in the electronics industry
would not appear to be applicable to a gold mining industry. This is due,
in part, to the fact that for the Leibovitz et al. process to provide a
commercially viable gold extraction and refinement method, its processes
would need to be different and would need to be accelerated by at least an
order of magnitude or more to be economically viable. In addition,
substantially changes would have to be made to the Leibovitz et al.
process in order to provide the ability for continuous or semi-continuous
ore processing and extraction of gold from the liquid chemicals.
DISCLOSURE OF THE INVENTION
The present invention includes process and systems and for efficiently,
rapidly, and safely extracting and refining gold from ores. The processes
and systems have many advantages over the aforementioned cyanide
extraction processes in that it uses more benign and less expensive
chemicals, has many fewer process steps, and permits the recycling and
re-use of its chemicals, thereby lowering the costs further and minimizing
environmental damages.
The present invention is preferably implemented as a two part process. In a
first part, gold is dissolved from the ore as a solution, and in the
second part the gold is removed from the solution. Briefly, gold is
extracted from the ore and dissolved in the chemical solution to form a
gold complex. Next, the complex is reduced to gold from the solution,
preferably by one of two methods. The first method precipitates the gold
complex by washing and decomposing of the gold complex to form pure gold.
The second method electrolytically plates the gold from the gold complex
solution onto a cathode to obtain pure gold.
More particularly, the first part of the process begins with the mining of
gold ore and the grinding of the ore to create fine particles. This
finally ground ore is deposited in an agitator tank (also known as the
"reaction chambers", "reaction vessels", "main vessels", and the like) and
is heated to an elevated temperature.
Preferably, the etchant (or "liquid", or "liquid chemical", or "solution")
is a KI-water solution with an addition of I.sub.2, and with an optional
addition of Isopropyl alcohol. The etchant, agitation, and elevated
temperature creates a gold complex in the etchant solution which is
extracted for further processing.
As noted above, this further processing can comprise of one of two methods.
In a first or "precipitation" method, the gold complex solution is
deposited in a cooling chamber at about 2.degree. C. This causes a black
precipitate of AuI.KI.sub.3 to form. This black precipitant is then
filtered and washed with water to create yellowish precipitate of AuI. The
yellowish precipitant is filtered and dried, and is thermally decomposed
to create the gold. In an alternative second method, the gold complex
solution is extracted, cooled if necessary, and water is added to create a
precipitant of AuI. This precipitate is filtered, dried and then thermally
decomposed into gold. During either of the described precipitation
methods, the chemical used in the process can be recycled and reused. For
example, the KI and the I.sub.2 can be reclaimed and recycled.
In a second of "electrochemical" method, the gold complex solution is
placed into an electro-extraction chamber at a temperature that is
preferably at or below that of the reaction chambers. Next, one or more
electro-extraction cells are immersed and activated in the etchant liquid
and an electro-deposition begins. In this method, the gold forms on the
cathodes of the cell. After the gold has been substantially
electrochemically removed from the etchant liquid, the electro-extraction
cells are removed and the cathodes are washed with water and filtered to
obtain the gold.
The systems and apparatus of the present invention are designed to
economically implement the above-described processes. A plurality of
reaction chambers (e.g., 8 reaction chambers) can be used for continuous
gold production. Since the method of the present invention is,
essentially, a two part process, the system of the present invention
preferably includes a first part processor which extracts the gold out of
the ore to put it into a gold complex solution, and a second part
processor which removes the gold from the gold complex solution.
A major advantage of the present invention is that it uses more benign and
less expensive chemicals. The elimination of the cyanide used for cyanide
processes and the mercury used in the amalgamation processes greatly
improves operator safety and reduces environmental damage. Furthermore,
the total chemicals used by the present invention tend to be less
expensive than the total chemicals used in the aforementioned processes,
and are well suited for recycling, again lowering costs and reducing
potential environmental damage.
In addition, the process of the present invention has many fewer steps than
the dominant cyanide extraction process of the prior art. This greatly
lowers the cost of production and increases the through put of the gold
extraction system.
These and other advantages of the present invention will become apparent
upon reading the following detailed descriptions and studying the various
figures of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flow-diagram of a prior art cyanide process for extracting gold
from ore;
FIG. 2 is a block-diagram of a system in accordance with the present
invention for extracting and refining gold from ore;
FIG. 3 is a flow-diagram of a first part process of the present invention;
FIG. 4 is a top-elevational view of reaction chamber of FIG. 2;
FIG. 4a is cross-sectional view taken along line 4a--4a of FIG. 4;
FIG. 5 is a block-diagram of a gold remover of FIG. 2;
FIG. 6a is a flow-diagram of a first preferred method ("first precipitation
method") for removing gold from solution implemented by the gold remover
of FIG. 5;
FIG. 6b is a flow diagram of an alternative first preferred method ("second
precipitation method") for removing gold from solution implemented by the
gold remover of FIG. 5;
FIG. 7 is a block-diagram of an alternative gold remover of FIG. 2;
FIG. 8 is a flow-diagram of a second preferred method ("electrochemical
method") for removing gold from solution implemented by the gold remover
of FIG. 7;
FIG. 9 is an illustration of electrolysis chamber of FIG. 7;
FIG. 10 is a flow-diagram of a process for purifying dore into gold in
accordance with the present invention; and
FIG. 11 is a cross-sectional view of a reaction chamber for converting dore
into gold in accordance with the process of FIG. 10.
BEST MODES FOR CARRYING OUT THE INVENTION
FIG. 1 is a flow-diagram of a prior art cyanide process for extracting gold
as discussed above. In FIG. 2, system 26 in accordance with the present
invention for extracting and refining gold from ore includes a first part
processor 28 and a second part processor 30. The first part processor 28
implements a first process which creates a gold complex in a solution. As
used herein "solution", "liquid", "liquid chemical", "etchant", and
variants thereof may be used synonymously. The second part processor 30
removes the gold from the solution and refines ("purifies") the gold to a
purified form. If necessary, an additional purifier 32 using one of the
aforementioned prior art methods can further refine the gold. Preferably,
a recycle chamber 34 is used to recycle the chemicals in the system 26.
The chemistry of the two part process of the present invention has
similarities to the chemistry and processes described in the
aforementioned U.S. Pat. No. 5,221,421 of Leibovitz et al., the disclosure
of which is incorporated herein by reference for all purposes.
The first part processor 28 preferably includes a reaction chamber 36, a
holding tank 38, a filter 40, and a pre-heater 42. A valve 44 may be
opened to allow fresh chemicals to enter an inlet 46 and/or to allow
recycle chemicals to flow in through valve 44 into a pipe 48. A valve 50
allows chemicals to flow from either pipe 48 or a pipe 52 into a pipe 54
and through a filter 40. From there, the chemicals flow into a pipe 56 and
through a pre-heater 42 before entering the reaction chamber 36 via pipe
58. Finely ground ore is also deposited in the reaction chamber 36 as
indicated at 60.
The output of the reaction chamber flows through a pipe 62 to a valve 64
which can divert the fluid to either holding tank 38 via a pipe 64 or to a
pipe 66. A valve 68 allows either the fluid flow from pipe 66 to a pipe 70
or from the holding tank 38 through a pipe 72 to the pipe 70. A valve 74
allows the liquid to be diverted to either pipe 52 or to an output pipe
74.
The output pipe 74 is coupled to the gold remover 30 which produces gold as
indicated at 76. While this gold can be quite pure, if additional
refinement is desired, the additional purifier 32 can create even purer
gold as indicated at 78. Optionally, chemicals extracted by the gold
remover 30 can be pumped to a recycle chamber 34 via pipe 80 where it is
mixed with "make up" chemical 82 in the recycle chamber. The recycle
chemicals in a pipe 84 can be used instead of, or it can be mixed with the
fresh chemicals flowing into the inlet 46 as determined by the position of
the valve 44.
In operation, the system 26 is charged with fresh and/or recycle chemicals
such that the reaction chamber is full and such that the various types of
the first part processor 28 are full. Ore is then put into the reaction
chamber 36 as indicated at 60, and the solution is pumped through the
first part processor 28 by a pump (not shown) in the direction indicated
at 86. That is, the solution is pumped from the reaction chamber 36
through pipes 62, 66, 70, 52, 54, filter 40, pipe 56, pre-heater 42, and
pipe 58 back into the reaction chamber 36 on a preferably continuous
basis. The solution preferably be pumped in this fashion for a number of
hours (e.g., 4 hours) until most of the gold that is going to be extracted
from the ore has been extracted from the ore. This can determined by a
titration process wherein the rate of change of dissolved gold can be
monitored, or by an in-line process (not shown) which automatically
terminates the process when it is determined that enough gold has been
extracted from the ore 60.
The holding tank 38 can be used for a variety of purposes. For example, the
holding tank can hold the gold complex liquid when exchanging ore at the
reaction chamber. Furthermore, the holding tank can hold water used for
washing the ore before its exchange, since the wash water can also include
gold. In addition, the holding tank allows the reaction chamber(s) to be
emptied for maintenance. While a precipitation chamber could be used for
this purpose, the liquid might not yet contain sufficient Au for
precipitation, or the precipitation chamber already be in use at that
time.
Once it is determined that there is sufficient gold complex in the solution
a valve 74 causes a gold complex solution to flow through pipe 74 and into
the gold remover 30. The gold remover 30 creates the gold 76 and,
preferably recycles the chemicals through recycle chamber 34 to be used in
the first part processor 28 again. The second part processor (gold
remover) 30 can produce gold of high purity but, if even higher purity is
desired, an additional purifier 32 can be used to produce highly purified
gold 78.
FIG. 3 illustrates a process 88 implemented by the first part processor 28
of FIG. 2. The first part process 88 begins at 90 with a mining of the
gold ore and with a step 92 where the ore is ground to the consistency
between that of a coarse sand and small pebbles. In a step 94, a KI+water
solution is prepared and is mixed with I.sub.2 in a step 96. Optionally,
Isopropyl alcohol is mixed with the KI and the I.sub.2 to server as an
accelerant. This mixture becomes the initial extraction solution. A step
98 adds the extraction solution to the ore in the agitator tank (i.e. the
main reaction chamber) at elevated temperature. This causes the gold to be
extracted from of the ore to become a part of a gold complex compound in
the solution. Next, in a step 100, the liquid with dissolved gold complex
compound is extracted for further processing and the process 88 is
completed.
FIG. 4 is a top-plan view of reaction chamber 36 in accordance with the
present invention. This particular embodiment of a reaction chamber is a
multi-vessel embodiment including 8 reaction vessels 102. The reaction
vessels 102 are enclosed in jackets 104 that are used for heating the
contents of the vessels 102, and the reaction vessels 102 are also
contained in a larger outer container 106 for containment purposes. Each
of the vessels has an agitator, an etchant inlet, a water inlet, and an
ore inlet. The various components of the reaction chamber 36 can be seen
in greater detail in the cross-sectional view of FIG. 4a.
The reaction vessels 102 are made from an inert, strong material such as
polyethylene. Alternatively, a composite material (such as metal covered
with plastic or ceramic), or an entirely ceramic vessel can be used. The
reaction vessel should be inert to KI, I, and Isopropyl alcohol. The
jackets 104 are used to heat the contents of the reaction vessels 102 and
can comprise electrical resistance coils, or fluid heating coils.
Alternatively, the containment vessel can include a heated fluid for
heating the contents of the reaction vessels, or use immersion heaters
(not shown) immersed in the solution of the reaction vessels.
The reaction vessels are located within the containment vessel 106 and are
supported pedestals 108. The outer container 106 can provide a rocking,
vibrating, or shaking motion help agitate the solution within the reaction
chamber 102. The pedestals fit within receptacles 110 of the container
106. Outlets 112 of the reaction vessels 102 are aligned with
corresponding outlets 114 of the containment vessel 106. Gaskets 116 are
made from an inert material and separate any bath liquid (e.g., hot water)
that may be in the outer container 106, or any liquids that may have
sloshed into the outer container 106, from the etchant liquid coming out
of the outlet 112. A filter 118 is preferably used to filter the fluid
flowing out of the outlet 112 to remove some of the ore sludge and larger
particulates. The material of the separator filter 118 is preferably
similar to the reaction vessel material and should be thick enough to
support the ore and the etchant mixture. Polyethylenes and other strong,
inert plastics are suitable for this purpose. Alternatively, a composite
material such as a strong metal converted with an inert plastic or ceramic
material can also be used to make the filter 118.
Associated with each reaction chamber is a mixer 120 which is also made
from a suitable, inert material such as polyethylene. The mixer has a
number of blades 122 and is rotated by a motor 124. There are a number of
water inlets 126 coupled to water sources by valves 128 and a number of
chemical inlets 130 coupled to the chemical solution by valves 132.
Preferably the water and chemical inlets take the form of spray heads so
that the liquids can be quickly and evenly applied to the ground ore
within the reaction vessels.
Temperature of the reaction chemicals in the reaction chamber(s) are
preferably maintained at a controlled temperature between room temperature
(e.g. 25.degree. C.) and 100.degree. C., with a preferred temperature of
the reaction at around 50-60.degree. C. The reaction vessel can be heated
by a variety of methods. For example, the reaction vessel can be heated
heating from outside using electro-resistive heating elements, or by hot
liquid carrying heating coils, or by a liquid bath, or by immersion
heaters inside the reaction chamber. The etchant liquids are preferably
pre-heated to the aforementioned controlled temperature, and the ores can
optionally be pre-heated (especially if they are to be roasted, i.e.
preheated in air). Insulation of the reaction chambers is preferably
sufficient to keep the temperature of the reaction chamber high enough to
carry out the reaction at a suitably high rate.
Agitation is preferred to intimately mix the ground ore with the chemicals
to promote the reaction to occur to at a relatively fast pace, and to a
desirable level of completeness. Agitation enhances the provision of fresh
chemicals to the reaction interface between the ore surface and the liquid
etchant solution. Agitation of large tanks is achieved by existing
techniques known in the art of element extraction from ores. In the case
of a large reaction vessel, the whole tank can be an agitation bed, and in
the case of smaller reaction vessel approach, multiple reaction vessels
can be placed on an agitation bed.
As noted, incoming chemicals are preferably preheated, filtered and brought
into the reaction vessel through pipes again made of inert materials,
which can be similar to the inert materials used in the reaction
chamber(s). Insulating the pipes is advantageous to maintain the heated
temperature of the incoming liquids. It is preferred that the chemical
solution be sprayed onto the ore, again for the purpose of accommodating
quick intermixing between the ore and chemicals to help in increasing
reaction rates as well as to carry the reaction to completeness. Outgoing
chemicals are preferably drawn out from the bottom, and gross filters can
be provided to prevent the ores being carried out with the outgoing
chemicals. Again, the gross filters are preferably made of the
aforementioned inert materials. After the liquid solution is removed of
the reaction vessel, a second filtration may optionally be used to remove
particulates. The pipes carrying the liquid solution from the reaction
chamber are preferably insulated and/or heated to minimize the rate of
precipitation of gold complex on the walls of the outflow pipes.
In use, the ore is inserted into the reaction chambers 102 by a mechanism,
not shown. Apparatus for loading and unloading ores are well known to
those skilled in the art. The valve 132 is opened to permit the chemicals
to flow into the reaction chamber 102 where they are heated by jacket 104,
by hot water within chamber 106, or by another suitable heating method.
Motor 124 causes the agitator 120 to rotate, thereby stirring the solution
134 within the vessel 102. Gold is extracted from the ore 136 into the
solution 134 to form a gold complex solution which can flow into the
filters 118 and out the outlets 112 and 114.
In FIG. 5, a gold remover 30, in accordance with a first ("precipitation")
method of the present invention includes a gold filtration chamber 138 and
a heating chamber 140. The gold complex solution is entered into the gold
filtration chamber 138 and filtrate (gold precipitate) is removed from the
gold filtration chamber. The filtrate liquid can be recycled as described
previously. The filtrate is then inserted into the heating chamber 140
where it is decomposed into gold and I.sub.2, which is also recycled as
previously described.
There are several preferred methods that can be implemented by the gold
remover 30 illustrated in FIG. 5. A preferred first method is shown in
FIG. 6a. The process 140 begins at 142 with the extraction of the liquid
from the gold complex solution into a cooling chamber to cool to
approximately 2.degree. C. The result of this cooling step is a black
precipitate of AuI.KI.sub.3. Next, in a step 144, this black precipitate
is filtered, and washed with water. This produces a yellowish precipitate
of AuI. Next, a step 146 filters and dries the AuI precipitate, and a step
148 thermally decomposes the AuI to create gold. As noted, the I.sub.2
created by the thermal decomposition of the AuI can be recycled in a step
150 and other chemicals created from the filtering and drying step can
also be recycled in a step 152.
In FIG. 6b, an alternative first method for the gold remover 30 of FIG. 5
begins at 156 with the extraction of the liquid of the gold complex
solution. The solution is cooled if necessary, and water is added. This
creates a precipitate of the AuI which is then filtered and dried in a
step 158. The dried precipitate of AuI is then thermally decomposed into
gold in a step 160. Optionally, a step 162 can recycle the I.sub.2 from
the step 160, and in a step 164 can recycle the KI+I.sub.2 produced by the
step 158.
An alternative embodiment for a gold remover 30' of FIG. 2 is illustrated
in FIG. 7. Instead of using a precipitation and filtering process, an
electrolysis process is used. The alternative gold remover 30' includes an
electrolysis chamber 166 and a wash and filter apparatus 168. The gold
complex solution is placed into the electrolysis chamber 166 which
produces a plated gold and, preferably, reclaims the chemicals of the
solution for recycling and reuse. The plated gold washed and filtered in
apparatus 168 to provide gold.
A second ("electro-chemical") process 170 implemented by the gold remover
30' or FIG. 7 is shown in FIG. 8. A step 172 extracts the liquid of the
gold complex solution into an electro-extraction chamber having a
temperature at or below that of the agitator tanks (i.e. the main reaction
vessels). Next, the electro-extraction cells are deposited into the
solution and gold is electro-deposited on the cathodes. Alternatively, the
cells can already be in the reaction chambers, and the gold complex
solution can be poured in around the cells, which are subsequently
energized by a power source to initiate the gold deposition on the
cathodes. Finally, in a step 176, the cathodes are removed and washed with
water, and the precipitate is filtered to produce substantially pure gold.
As an optional step 178, the chemical can be reclaim and recycled.
In FIG. 9, an electrolysis chamber 166 of FIG. 7 is illustrated in greater
detail. While in this embodiment two electro-extraction cells are
illustrated, it should be clear that more, and potentially many more,
cells can be used to speed up the extraction process. The chamber 166
includes an outer chamber 180, a reaction vessel 182, a heater jacket 184,
the gold complex solution 186, and one or more electro-extraction cells
188. Each of the electro-extraction cells 188 includes an anode 190 and a
cathodes 192. When energized by a d.c. power source (not shown),
preferably to about 3-5 volts d.c. and 20 amperes per liter of solution,
the gold and the gold-complex solution 186 will be plated on the cathodes
92. A current density of about 0.1 A/cm.sup.2 of cathode area is desired.
After the rate of plating in a cathode is diminished, or after some other
suitable end point criteria, the cells 188 are removed and the cathodes
192 are washed to produce substantially pure gold.
With reference to the foregoing descriptions, several preferred processes
in accordance with the present invention will be described. It will be
appreciated by those skilled in the art that the described processes are
illustrative of preferred embodiments of the present invention, and that
there are a number of equivalents that will be apparent to those skilled
in the art of the various processing steps, apparatus, systems, and
materials that are within the spirit and scope of the present invention.
Gold Ore Extraction and Refinement Process Examples
The process begins with the mining of gold ore, which is produced in large
quantities in, inter alia, South Africa, Russia, the United States of
America, Canada, Australia, and other nations. The ore is then finely
ground to between the consistency of coarse sand and fine pebbles in
commercially available or custom made ore grinders. Ore mining and
grinding processes are well known to those skilled in the art. Next, a
solution of I.sub.2 +KI(aq) and preferably Isopropyl alcohol is added to
the ore, or vice versa. Again, the loading and unloading of ores is well
known to those skilled in the art. The solution is preferably made by
dissolving commercially available KI crystals in water to make KI(aq), and
then dissolving commercially available I.sub.2 crystals in the KI(aq).
Optionally, but preferably, Isopropyl alcohol is then added to the I.sub.2
+KI(aq) to serve as an accelerant. Other alcohols can also be used as
accelerants. The Isopropyl alcohol can accelerate the gold dissolving
process by 100%. One part Isopropyl alcohol (IPA) can be added to one part
KI(aq) to create IPA.KI(aq). IPA increases the solubility of gold complex
and hence increases the reaction rate a desirably rapid rate. It should be
noted that since the IPA accelerates the process, it would not be a
suitable addition for a controlled rate process. The reaction rate of the
present invention can also be increased by increasing the flow rate of the
solution through the ore.
The solution and ore should be mixed in a reaction vessel made of an inert
material to the various chemicals of the process. For example, a
polyethylene material, composite materials made of ceramic or metal coated
with a suitable plastic or inorganic coating (such as ceramic) can be used
for constructing the reaction vessel. The reaction vessels require a
material that can sustain repeated use, but is not attacked by the
etchants. Smaller tanks, made of similar material can also be used.
Depending on whether a large tank is used or small tank is used, the
approaches of loading of fresh ore, and unloading of spent ore will be
different, as appreciated by those skilled in the art. The chemical
addition and removal, to a large extent may be similar but with
modifications, as will be apparent to those skilled in the art.
Gold from the ore is dissolved by the chemicals and a gold complex is
formed according to the following reaction:
2Au(metal)+[2I.sub.2 +2KI(aq)].fwdarw.2AuI.KI.sub.3 (aq)
where the "." between the I and K refers to a weak bond, and "(aq)" refers
to an aqueous solution.
At 40.degree. C., about 20 grams of gold can be dissolved in one liter of
the aqueous KI/I.sub.2 solution without IPA. With proper agitation, this
can be achieved in less than 45 minutes. As noted above, the inclusion of
IPA increases the solubility of the Au in the solution and also increase
the rate at which it goes into solution. As the solution becomes saturated
with gold, the gold extraction rate will decrease. Elevated temperatures
greater than about 30.degree. C. substantially increases the solubility,
and use of IPA while increases the reaction rate, and also positively
affects the solubility. Reaction times for extracting gold from the ore is
preferably several hours to ensure virtually all of the gold has been
extracted from the ore. A preferred temperature range for the reaction is
50-60.degree. C. as this will help extracting more gold per liter of the
solution.
Typically 3 tons of ore needs to be processed per ounce of gold, which is
also about the amount of gold that one liter of etchant can contain
without loss of reactivity. The same chemicals are preferably continuously
circulated with fresh batches of ore till the chemical reaches a
saturation point after which the gold complex can be precipitated at a
lower temperature. This technique reduces the quantities of chemicals
required. Also, after the gold is extracted from the etchant chemical,
whether by the aforementioned precipitation or electrochemical methods,
the chemicals are preferably be reclaimed and reused.
The etchant liquid (i.e. the gold complex solution) after it reaches a high
enough gold concentration, is transferred into a precipitation chamber in
the first methods, or to an electro-extraction chamber in the second
method. It is necessary to transfer the solution to a chamber other than
the main reaction chamber (vessel) in the first ("precipitation") methods
because of the temperature differences in the two parts of the process.
However, for the second ("electrochemical") method the process can be
carried out in the main reaction vessel(s). Nonetheless, it is preferred
that the electrochemical extraction be carried in separate chamber as it
makes the monitoring and maintenance of the two part process (i.e. gold
extraction from ore into solution, and the subsequent extraction of the
gold from the etchant) of the process separate, simple, and relatively
clean.
With the first (precipitation) method, etchant liquid enters a low
temperature chamber (preferably maintained at about 2.degree. C.), and
because of the solubility differences, the gold complex will precipitate
out. Even though the low temperature chamber will be in the loop for the
continuous operation, in practical terms it would be used as a batch
operation since the solubility gold in the etchant is quite high in
relative terms compared to the amount of gold in the ore. The liquid
etchant is preferably continuously recycled through the main reaction
chamber.
After the precipitation of gold complex, the liquid is filtered. The low
temperature precipitation chamber can be also be fitted as a filtration
chamber, or the precipitate can be transferred to a separate chamber for
filtration.
Addition of water (which is preferably cold) will convert the gold complex
AuI.KI.sub.3 into AuI. This can be accomplished during the filtration
process. Even more preferably, the cold water can be added to the aqueous
etchant solution contain the gold iodide-potassium iodide complex (black
precipitate), to cause the gold iodide to precipitate into an insoluble
compound even more readily. This helps in extracting the gold without
having to wait for the saturation of the etchant with gold complex, and
provides an option for continuous flow operation of the extraction of the
gold compound.
AuI (solid precipitate) thus collected can be readily converted to gold
after drying and heating the it to temperatures of about 140.degree. C. to
150.degree. C. to form relatively pure Au. I.sub.2 is a byproduct and is
fed back into the recycle loop. Gold can be further purified if necessary
by prior art methods, e.g. mercury amalgamation or cyanide processes.
However, since these prior art methods are being applied to substantially
pure gold, they will take place on a much smaller scale and with much less
negative side effects than when they were applied to the extraction of
gold from ore.
With the second (electrochemical) method, the gold is plated onto the
cathodes of the cells. The plated material can be washed off of the
cathodes with cold water at about 25.degree. C., and then filtered and
dried to provide substantially pure gold.
Another variation of the process transfers the gold etchant containing the
AuI.KI.sub.3 complex to a low temperature chamber (as described above),
and chilled water at a temperature of about 10-25.degree. C. is added to
cause the AuI to precipitate from the solution without the intermediate
step of the AuI.KI.sub.3 precipitation. AuI is insoluble in, and hence
precipitates out, of the solution at these temperatures and can therefore
be separated from the solution.
A further variation cools the etchant solution to a lower temperature than
the reaction temperature of the main vessel as it is removed from the main
vessel. For example, the etchant can be cooled to about room temperature.
It is then mixed with chilled water at about the temperature of
10-25.degree. C. and fed into a filtration chamber. Gold iodide
precipitates and is and collects as filtrate on the filter. The etchant
liquid is the preferably fed back to the recycle loop.
In FIG. 10, a process 194 for refining gold from dore is illustrated. In a
first step 196, the dore is dissolved in an etchant which serves an
electrolyte for an electro-extraction cell. A step 198 then causes the
gold from solution to plate the electrode of the cell, and a step 200
washes and filters the precipitant from the plated cathode of the cell to
produce pure gold.
In FIG. 11, a system 202 for converting dore to gold includes a containment
vessel 204, a reaction vessel 206, and an electro-extraction cell 208, and
a solution 210. A rod of dore 212 is slowly dissolved in the etchant 210,
which is preferably a KI+I.sub.2 (aq) solution to create a the
electrolyte. The cell 208 is coupled to a power supply of approximately
3-5 volts d.c. capable of providing 20 amperes/liter of solution to cause
the gold 212 to plate upon the electrode 214 of the cell 208. Preferably,
hot water 216 is circulated between the containment vessel 204 and the
reaction vessel 206 to maintain the temperature of the dore solution 210
at about 30-50.degree. C. The water can flow out of an outlet 218.
Likewise, fresh etchant solution can flow in an inlet 220 and out of an
outlet 222 to provide fresh electrolyte solution.
After the gold has been extracted and refined, it may be fashioned into
ingots or other suitable forms. The gold may be alloyed with other metals,
and fashioned into a number of articles of manufacture, including jewelry.
The gold may also be used in its purified form for commercial and
scientific purposes, or fashioned into other forms for use as coinage,
bullion, etc.
While this invention has been described in terms of several preferred
embodiments, there are alterations, permutations, and equivalents which
fall within the scope of this invention. It should also be noted that
there are may alternative ways of implementing the process, methods,
systems and apparatus of the present invention. It is therefore intended
that the following appended claims be interpreted as including all such
alterations, permutations, and equivalents as fall within the true spirit
and scope of the present invention.
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